In an AC surface discharge type panel that is typical as a plasma display panel (hereinafter abbreviated as a “panel”), a number of discharge cells are formed between a front plate and a back plate arranged to be opposite to each other.
The front plate includes a front glass substrate, display electrodes composed of a pair of scan electrode and sustain electrode, a dielectric layer and a protective layer. The plurality of display electrodes are formed in parallel with one another on the front glass substrate. The dielectric layer and the protective layer are formed on the front glass substrate so as to cover the display electrodes.
The back plate includes a back glass substrate, data electrodes, a dielectric layer, barrier ribs and phosphor layers. The plurality of data electrodes are formed in parallel with one another on the back glass substrate. The dielectric layer is formed on the back glass substrate so as to cover the data electrodes. Furthermore, the plurality of barrier ribs are formed in parallel with the plurality of data electrodes, respectively, on the dielectric layer. The phosphor layers are formed on a surface of the dielectric layer and side surfaces of the barrier ribs.
Then, the front plate and the back plate are arranged to be opposite to each other such that the plurality of display electrodes intersect with the plurality of data electrodes in three dimensions. A discharge space is formed between the front plate and the back plate. The discharge space is filled with a discharge gas. Here, the discharge cells are formed at respective portions where the display electrodes and the data electrodes face one another. In the panel having such a configuration, ultraviolet rays are generated by a gas discharge in each discharge cell. The ultraviolet rays cause phosphors of R (red), G (green) and B (blue) to be excited and to emit light, thus performing color display.
A sub-field method is employed as a method for driving the panel. JP 2000-242224 A (hereinafter referred to as Patent Document 1) discloses a new driving method of sub-field methods in which light emission that is not involved in a gray scale display is suppressed to the minimum to improve a contrast ratio.
In the following description, one field period is divided into N sub-fields each having a setup period, a write period and a sustain period. The divided N sub-fields are abbreviated as a first SF, a second SF, . . . and an Nth SF. According to the driving method of Patent Document 1, in the N sub-fields excluding the first SF, setup operations are performed only in discharge cells that have lighted up in sustain periods of respective preceding sub-fields.
Specifically, in the first half (a first period) of a setup period of the first SF, a ramp waveform gently rising is applied to the scan electrodes to generate weak discharges, and wall charges necessary for a write operation are formed on each electrode. At this time, excessive wall charges are formed in anticipation of optimization of the wall charges performed later. Then, in the second half (a second period) of the setup period, the ramp waveform gently dropping is applied to the scan electrodes to again generate weak discharges. In this manner, the excessive wall charges stored on each electrode are weakened, so that the amount of the wall charges on each discharge cell is adjusted to an appropriate amount.
In a write period of the first SF, write discharges are generated in discharge cells that are to emit light. Then, in a sustain period of the first SF, sustain pulses are applied to the scan electrodes and the sustain electrodes to generate sustain discharges in the discharge cells in which the write discharges have been induced, and the phosphor layers of the corresponding discharge cells are caused to emit light, thereby performing image display.
In a setup period of a subsequent second SF, a driving waveform that is the same as that in the second half of the setup period of the first SF, that is, a ramp waveform gently dropping is applied to the scan electrodes. Thus, formation of the wall charges necessary for the write operation is performed concurrently with the sustain discharges. This eliminates the necessity of independently providing the first half, which is the same as that in the setup period of the first SF, in the setup period of the second SF.
As described above, the ramp waveform gently dropping is applied to the scan electrodes, so that the weak discharges are generated in the discharge cells in which the sustain discharges have been performed in the first SF. Accordingly, the excessive wall charges stored on each electrode are weakened to be adjusted to wall charges appropriate for each discharge cell. In the discharge cells in which the sustain discharges have not been generated, the weak discharges are not generated since the wall charges are held in a state at the end of the setup period of the first SF.
As described above, the setup operation of the first SF is a setup operation for all cells that causes all the discharge cells to discharge, and the setup operations of the second SF and the subsequent SFs are selective setup operations that set up only the discharge cells in which the sustain discharges have been performed. Accordingly, in the discharge cells that are not involved in image display (the discharge cells that do not emit light) of all the discharge cells, the weak discharges are generated only in the setup period of the first SF, and the weak discharges are not generated in the setup periods of the other SFs. This enables the image display with a high contrast.
In addition, a driving method in which data pulses are applied to the data electrodes in the first period is disclosed in JP 2005-321680 A (hereinafter referred to as Patent Document 2) as a method of stabilizing the setup discharges when the foregoing setup operation for all the cells is performed. According to the driving method of Patent Document 2, in the first period of the setup period for all the cells, a positive data voltage is applied to the data electrodes to generate discharges between the scan electrodes and the sustain electrodes before discharges between the scan electrodes and the data electrodes, so that the setup discharges can be stabilized and image display with an excellent quality can be performed.
Furthermore, JP 2004-163884 A (hereinafter referred to as Patent Document 3) discloses a method of suppressing unnecessary discharges in the setup operation for all the cells to improve the contrast.
According to the driving method of Patent Document 3, the sustain electrodes are separated from a ground terminal and a node (high impedance state) in a certain period, in which the ramp waveform gently rising is applied to the scan electrodes, of the first period. In this case, the ramp waveforms are applied to the scan electrodes and also to the sustain electrodes. This decreases a potential difference between the scan electrodes and the sustain electrodes to suppress unnecessary discharges, thereby improving the contrast.
[Patent Document 1] JP 2000-242224 A
[Patent Document 2] JP 2005-321680 A
[Patent Document 3] JP 2004-163884 A